1. Field of the Invention
The present invention relates to a primer as a marker for selecting an Aphanomyce cochlioides-resistant plant variety and a selection method therefor, an Aphanomyce cochlioides-resistant variety acquired through the aforementioned method, and a methodology for identifying an Aphanomyce cochlioides-resistant gene.
2. Description of the Related Art
The Aphanomyce cochlioides are developed through a type of soil-borne fungus that infects plants of the Beta genus, such as Beta vulgaris L., etc. as crops for sugar manufacture. It is difficult to prevent and eliminate such damage. Major disease characteristics thereof include damping-off disease of seedlings in which seedlings die in an upright position during the seedling stages, and root rot symptoms in which humid black spots as shown in FIG. 1 appear in a root section during a later growth stage and rot is caused thereto (non-patent document 1). Major damage includes reduction of crop yields of Beta vulgaris L. at the point of production thereof and the infecting of Beta vulgaris L. by affected Beta vulgaris L. within piles, etc. Furthermore, disease damage extends to mixtures including rotten roots in the sugar manufacturing process and reduction of sugar yields in the sugar manufacturing industry. All such damages have become major issues (non-patent document 2).
Methods of control of such disease have been studied in the U.S.A, Japan, and Europe. However, no effective method has yet been found. For instance, the improvement of water permeability and drainage of agricultural fields of Beta vulgaris L., the search for active medical agents, and the selection of resistant plant variety have been reviewed. However, in relation to improvement of water permeability and drainage of agricultural fields, huge investments upon undertaking of construction may be necessary, which would make it difficult to realize the same. Additionally, in relation to control based on medical agents, there are no specifically effective agents at present. Furthermore, it is problematic that the root portion is a diseased area resulting from the disease, and therefore, medical agents are not sufficiently able to circulate therein. Selection of a resistant plant variety would seem to be the most effective measure for controlling such disease. However, a method for selection of a resistant plant variety based on the conventional art depends on root phenotypic disease symptoms. Therefore, problems have been caused when affected stocks that did not show accidental disease symptoms due to influence of environmental factors, etc., have been wrongly judged as resistant stocks, and selection also requires enormous efforts, time, and costs.
The Beta vulgaris L. market is enormous, exceeding 860,000,000,000 yen per year throughout the world. Aphanomyce cochlioides could have a great influence on crop yields of Beta vulgaris L., and by extension, could have a major influence on the supply amounts of raw materials for sugar manufacturing. Thus, the impact on the market is immeasurable. Accordingly, in the breeding industry in Europe, breeding of an Aphanomyce cochlioides-resistant plant variety is an object of focus, and this involves spending enormous costs, time, and efforts, even at present. However, it has been impossible to obtain effective study outcomes regarding Aphanomyce cochlioides-resistant varieties and Aphanomyce cochlioides-resistant genes to date.    Non-patent document 1: Tsutomu Kajiyama and Fumio Tanaka, proceedings of Japanese Society of Sugar Beet Technologists, 2000, 42:59-63.    Non-patent document 2: Kazunori Taguchi, Naoki Oogata, and Masakatsu Tanaka, proceedings of Japanese Society of Sugar Beet Technologists, 2001, 43:36-43.    Non-patent document 3: Vos P, et al., Nucleic Acid Res., 1995, 23:4407-4414